It is estimated that at the end of a secondary oil recovery process, only about 30% to 40% of original oil reserve is recovered, while the rest of the crude oil is retained in the formation due to a competition process between capillary and viscosity forces.
The recovery of the remaining 60% to 70% can be achieved by unconventional methods that generally are classified as Enhanced Oil Recovery, or EOR, which are used for obtaining any additional production by introducing artificially produced energy within the site. Thus, some processes within this category are water injection, high pressure gas and steam injection, as well as chemicals injection. Other EOR processes and their combinations involve the introduction of additional thermal energy. One of the most effective chemical processes is the injection of surfactants using micellar solutions for micro emulsions formation.
Also, the dispersion of some chemical species are common in the oil recovery processes and they find a wide range of applications to modify the properties of heavy crude oils, thus making it lighter crudes in terms of viscosity and for reducing the level of contaminants like sulfur and metals, which improves the flow overall and makes it to flow easily to the surface.
Micro emulsions are micellar solutions with the characteristics of surfactant type solutions. The degree of applicability will depend on the characteristics of the surfactant and its behavior with respect to some system variables.
Previous works report some methods for micro emulsions preparation, for example European Patent 2 096 411 T3 describes the preparation of a microemulsion as a flavor enhancing agent that does not require any mixing stage for application in the food industry. Also, it favors microemulsion formation of other flavor enhancing mixtures of immiscible foods and triglyceride type oils, together with the interaction of a hydrophilic surface active agent.
U.S. Pat. No. 4,146,499 discloses a method of dispersing an immiscible liquid in the aqueous phase to form a microemulsion. The method includes the stage of selecting a primary surfactant that is amphiphillic, together with a surface active agent that is used in a liquid that is water immiscible, which is dispersed in another liquid that is water immiscible. Thus, a surface active agent in the aqueous phase has to disperse the immiscible liquid, and a secondary surfactant in the aqueous phase is used, which has a HLB (Hydrophilic-Lypophilic-Balance) higher than the parent surfactant.
U.S. Pat. No 4,557,734 discloses production of hybrid micro emulsions of fuel that are prepared from vegetable oil, such as seed of soybean oil, methanol or ethanol, a straight chain isomer of octanol, and optionally, water. It describes the production of fuels using 2-octanol, anhydrous methanol and soybean seed oil. Also, it proposes mixing triolein, different individual alkanols C4-C14 and water, to provide a composition which is water tolerant.
U.S. Pat. No. 5,045,337 describes some micro emulsions that are thermodynamically stable, transparent and uniform, which are prepared from a polar solvent, a monoester and a specific di-ester of polyglycerol and a lipid. The microemulsion of this patent contains 90% to 99.8% of a lipid material and approximately 0.1% to 5% of a polar solvent. The polar solvent can be selected from water, glycerol, propylene glycol and di-propylene glycol.
European patent DE 2829617 C2, describes a microemulsion for use in oil recovery methods, especially useful under high salinity water conditions. These include a water mixture that contains an excess of monovalent and di-valent salts, a hydrocarbon, an amphoteric surfactant that contains nitrogen compounds and a co-surfactant agent comprising at least one alcohol with C1C10 chain.
Venezuelan Patent A042819 of October 1985 discloses a method for oil recovery, where a microemulsion with a superior phase or with intermediary phase and an immiscible aqueous phase are simultaneously injected into an underground formation. The viscosity of the injected phase is adjusted in such a way that the relationship between their viscosity and the one for the aqueous phase microemulsion viscosity approaches the brine/oil viscosity ratio of the site.
U.S. Pat. No. 3,981,361 dated Sep. 21, 1976, describes a method for oil recovery from subterranean formations using a micro emulsion, where the surfactant added to the solution is a dodecyl-benzene-sulfonate of xylene monoethanolamine salt and the co-surfactant is a tertiary Amyl alcohol.